Tag: normal form

How (And How Not) to Decompose Relations

When you read about normalization you usually get the set of conditions that a database in the nᵗʰ normal form should satisfy and the set of rules, a sort of a cook-book, for obtaining that normal form. But why these rules are safe to apply to your denormalized relations is a skip material. Here, I would like to present some elementary concepts on how we decompose relations and what can go wrong.The concepts I want to present may seem a bit complicated but, on the other hand, they are so basic that you rarely see it written. Still, they are essential for understanding how the normalization process works. One may prepare a perfect meal just by following a recipe but no one can master the art of cooking without understanding what’s going on behind-the-scenes. The same holds true with databases.

The Boyce-Codd Normal Form (BCNF)

Why do you need all of this normalization stuff? The main goal is toavoid redundancyin your data. Redundancy can lead to various anomalies when you modify your data .Every fact should be stored only onceand you should know where to look for each fact. The normalization process brings order to your filing cabinet. You decide to conform to certain rules where each fact is stored.Nowadays the go-to normal forms are either the

On Keys

Today we continue our series of posts on data normalization. In the previous post on data normalization I explained what functional dependency is. Today we will talk aboutcandidate keysin a table.A candidate key is a set of columns such thatall other columns in the table are dependent on it, and the set isminimal, that is if you remove a column, then the resulting set is not a candidate key.Example: Table Person

On Functional Dependencies

Do you remember the post about update anomalies ? I promised you we’d explain how to design tables which have no update anomalies. So here we go!Today we begin a series of posts on data normalization. We will talk aboutfunctional dependencies, a concept that needs to be explained before we dive deeply into database schema normalization.The subject is rather abstract and theoretical but I will try to restrain myself from going too deep into mathematics. I will try to keep things simple and down-to-earth. (The operative word being try ;) )